The present invention relates to an apparatus for measuring the weight per unit length of a cigarette rod in a cigarette-making machine, and more particularly to such an apparatus which has means for centrally positioning the rod to effect an accurate measurement.
In a cigarette-making machine, tobacco is formed within a continuous tube of paper to give a rod which is cut into individual cigarettes. Measurement of the cigarette rod weight per unit length is made at the continuous rod stage so that an indication can be obtained for control purposes and automatic weight control and inspection and other measurements of weight variation can be effected. The weight measurement is made by passing radiation from a radio-active isotope through the rod to a radiation detector, the degree of radiation absorption being an indication of average weight. In practice, the radiation source must be small and the cigarette rod must run close to the source. Minor variations in the position of the rod affect the radiation transmission and give rise to errors in weight determination. Generally, the rod is supported in a tube which may have a thin-walled window or a space at the radiation area. The tube should be small in diameter to restrict lateral movement of the rod. However, the rod may have irregularities in shape or diameter which cause the rod to snag and tear on small guide tubes. Guide tubes at present are therefore larger than is required for very accurate weight measurement. The present invention seeks to overcome this difficulty.